Biomass Energy Systems

Providing modern Biomass-fired energy systems and related equipment for industrial clients worldwide.


Sigma Thermal provides complete packaged biomass systems for industry.  The design, engineering, and manufacturing of our systems are backed by decades of energy experience. Packaged biomass energy systems incorporate a fuel feed system, ash handling system, and electric automation controls. Installation supervision, training, parts, and equipment service management are provided to help maintain and support efficient operation for the life of the system.

Reciprocating Grate Furnace Design

The Sigma Thermal reciprocating grate furnace is the most effective design for complete combustion of waste materials with low heating value, high moisture content, and high ash content. Our design allows for finite combustion control, minimizing emissions and utilizing a large range of different waste fuels, with varying characteristics (i.e. chemical composition, fuel size, and moisture content).

Biomass Energy Systems

Biomass-Fired Combustion System

Wet Fuel Furnace

Used largely in the wood products industry, where higher moisture content fuels such as hogged bark and green wood chips are available. The reciprocating grate achieves gasification through the staged combustion of wet fuel. rendering-biomass-wet-fuel-furnace-ox10241Our grate is divided into multiple sections, allowing for varying speeds and controlled underfire air zones, resulting in the combustion of your fuel in a manner that is considered to be more complete.  Depending on the moisture content of the fuel, the grate reacts to obtain the maximum energy amount from the fuel.  This prevents the over burning of dry fuel and the underutilization of wetter fuels by altering the amount of time the fuel spends on the grate.

Dry Fuel Furnace

Dry Fuel Burner - Underfeed Stoker Furnace

A dry fuel furnace design is available for processes in which the available fuel is of a dryer content. A screw controls the feed rate to a pile burner, completely encircled by rows of centrifugal combustion air nozzles to ensure an even combustion of all the fuel.

Secondary Combustion Chamber

rendering-secondary-combustion-chamber-ox10241Retention time is an extremely important factor of combustion that is often overlooked in a quality combustion system, and true complete combustion requires this to be considered. Our secondary chamber is designed for each job in order to ensure ideal combustion.

The result is lower emissions, maximized energy transfer, and total utilization of the potential energy available in your fuel.

Suspension Burner

Suspension burners can be used in addition to our Wet and Dry Furnace designs, or as a single unit combusting finer materials such as sander dust. The material is blown through high-pressure tubing into a centrifugal burner. The burner makes use of primary and secondary air, allowing adjustments to fuel consumption, as well as flame length and width.

Biomass-Fired Hot Gas Generator


Clean hot gas generation is available for systems requiring direct heat. Rotary dryers for the preparation of material to be used in OSB, MDF, Pelletizing, and others. Maximum combustion control results in fewer issues from sparks and dirty flue gas that are common with other systems.

Biomass-Fired Thermal Fluid Heater

Thermal fluid heating, sometimes referred to as thermal oil heating, is a type of indirect heating in which a liquid phase heat transfer medium is heated and circulated to one or more heat energy users within a closed loop system.

Thermal fluids offer the user the capability of high-temperature operation (up to 600F with organic thermal oils and 800F with certain synthetics) at very low pressures. Due to the low operating pressure and properties of thermal oils, most heaters are built to ASME Section VIII, and a licensed boiler operator is not typically required.

Biomass-Fired Steam Boiler

Steam generation from direct fired hot gas steam generators. Let our engineers take a look at the energy you have available and design a system to transfer that energy into usable steam for your process.

Thermal Oil to Steam Generation

Using a thermal oil heat exchanger, low-pressure steam generation can be achieved. Let our engineers take a look at the energy you have available and design a system to transfer that energy into usable steam for your process.

Biomass System Equipment

Biomass Fuel Feed System

A dependable fuel feed system is crucial to maintaining complete and thorough combustion control. Your fuel feed system should be as steady and worry free as possible.
Sigma Thermal offers a complete fuel feed package to support your furnace. Engineered to be as complete and turn-key as possible, the conveyors and fuel bins are designed to work specifically with your furnace to deliver exactly the amount of fuel required. This minimizes the waste of valuable fuel, along with ensuring that the energy needs of your plant are consistently met. In many plants, the fuel feed and combustion systems are engineered as separate packages, treating integration as an afterthought. This results in equipment wear and operation difficulties. Your system is unique and should be designed with the complete process in mind.

Wet Fuel Storage Bin


  • Rugged live bottom fuel feed design utilizing “ladders” for accurate feed rate control.
  • No screws in the base of the bin like popular silo designs. Our ladder design is more rugged and capable of handling larger pieces of varying fuel.
  • Hydraulic cylinders, motors, and power units are completely external to the bin. Minimal maintenance requirement and reduces costly downtime.
  • Range of sizes offered to meet feed requirements and operating schedule of your plant.

Fuel Feed Metering Bin

  • Hydraulically driven rams deliver precise amount of fuel required by the furnace at any time.
  • Locally dedicated hydraulic power unit designed with variable speed capability
  • Premium combustion control. No overfeeding or underfeeding.


Intermediate Storage Bin

  • Raised bin for the intermediate storage of fuel.
  • Located directly above the furnace metering bin and close to the mouth of the furnace.
  • Hydraulically driven ladders feed the fuel metering bin as required by the system.
  • Minimizes surges and gaps - Balanced fuel feed line.

Fuel Feed Conveyor

  • Heavy duty drag chain conveyor designed to handle hogged bark and large wood material.
  • Drag chain design utilizes double chain with angle and UHMW “sweepers
  • Constant and reliable feed to the system metering bin.

Ash Handling System

A clean process and emission controls are vital in any modern biomass combustion system. We integrate our systems with the best designs for controlling emissions and maintaining a clean facility.

Wet Submerged Ash Conveyor

rendering-wac-wet-submerged-ash-conveyor-ox10241The submerged ash conveyor collects ash from under a wood fired or biomass-fired energy system. The water level is controlled by a float switch and in a separate container that is connected via a bottom pipe to the conveyor to keep the float clean and the float switch activates a solenoid valve for makeup water to fill the conveyor and maintain water level. The bottoms of the ash hoppers are placed into the water of the conveyor to give the energy system an airlock as the energy system is operated under negative pressure. The submerged ash conveyor utilizes a bottom drag chain design and comes complete with gear box drive and motor. The ash conveyor drag chain and flights pull wet ash along the bottom of the conveyor and the chain and flights return on the top. The submerged ash conveyor is seal welded and has a tail end sprocket and drive shaft with chain sprockets at the discharge end. There is an incline of the conveyor to remove surface water from the ash and to allow for a discharge point to an ash bin. An idle sprocket is included to allow the drag chain to change direction from horizontal to incline.


The Multiclone is the primary flue gas cleaning device. A purely mechanical device for the removal of solid particles from your gas stream. Forcing the flue gas through a set of centrifugal cones causes the separation of the larger particles while allowing the clean gas to pass.

Water Cooled Ash Screw


This design provides a way to transport high-temperature ash from a wood-fired system or biomass-fired system without damaging the metal of the conveyor. The ash conveyor includes a jacketed housing (trough) for an ash screw to be cooled with water. In addition, the shaft of the ash screw is also cooled with circulating water in a closed water-cooled loop. Water first travels through a rotary union into the shaft of the screw and then exits the opposite end. Water also enters the jacketed screw housing (trough) and exits the opposite end of the housing. A single water connection is brought to the ash inlet end of the conveyor, and then the water line is split and connected separately to the screw shaft and the screw housing (trough). At the discharge end of the conveyor, the hot water is combined together again and goes through a cooling radiator and then is circulated back to the front of the ash screw in a closed-loop circuit.

Biomass Control Systems

Control systems for biomass-fired energy systems are complex due to the integration of fuel handling, combustion control, and ash removal.  It is imperative that all of these systems work in harmony together and are designed in such a way that gives operators maximum control while maintaining safe operation.  Sigma Thermal can offer complete control systems and/or integration support for all aspects biomass-fired energy systems.  Talk with our automation group to see how we can help you install a safe and effective control system.

Maintenance – Parts – Retrofit Services

Utilize our aftermarket services to support the operation of your biomass energy system throughout it’s lifetime.

Sigma Thermal provides maintenanceretrofit services, and replacement parts for biomass-energy systems. Our retrofit services include emission upgrades and system modifications. Retrofit services are also available for biomass-fired combustion systems built by other suppliers.

Biomass Energy System Site

  • Pre-Scheduled Maintenance
  • Replacement Equipment / Parts*
  • Energy Audits
  • Retrofit Emission Upgrades
  • Boiler MACT Compliance
  • Electric Automation Control

* GTS Energy system replacement grate bars available – no retrofit required. Contact us for details.

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